1. Field of the Invention
The present invention relates to aqueous dispersions containing fillers and/or pigments and novel dispersing agent mixtures.
2. Description of the Prior Art
Aqueous dispersions of fillers and/or pigments, which can be used, for example, as pigment pastes in coating compositions for buildings, generally have a solids content of 30 to 90 wt. %. The dispersing agent should impart suitable rheological properties to the dispersion at the desired solids content and, in the case of pigment pastes, the property of being readily incorporated into corresponding coatings and paints. The dispersing agent or wetting agent should also improve the wetting of the materials to be dispersed or wetted, facilitate deagglomeration during the dispersion process and stabilize the finished dispersion against agglomeration, sedimentation and flooding.
Organic and inorganic dispersing agents for these purposes are known. Phosphates, polyphosphates or sodium hexametaphosphate are used as inorganic dispersing agents.
Organic dispersing agents include polymers and copolymers of methacrylic and acrylic acid having a low to average molecular weight. DE-A 2,700,444 describes the use of copolymers of maleic acid derivatives; JP-A 57/095 396 describes the use of copolymers of acrylic acid and of styrenesulfonic acid; JP-A 56/115630 describes the use of copolymers of unsaturated sulfonic acids; and DE-OS 3,101,939 describes the use of phosphorus-containing polyacrylic acid copolymers. The use of sulfonated polyester resins is described in SU-A 861,377 and the use of derivatives of styrene-maleic anhydride copolymers is disclosed in SU-A 903,438. The use of low molecular weight non-ionic surfactants is described in BE-A 741,374.
The effectiveness of the known dispersing agents is in many cases not adequate to obtain pigment pastes and/or dispersions having optimal properties for technical use. If the viscosity of such pigment pastes and/or dispersions is too high, the solids content has to be decreased in order to obtain technically usable dispersions, for example, coating compositions to be applied by brushing. This leads, however, to deterioration in the quality of these paints, in particular their strength of color, covering power and/or film formation.
In the case of pigment pastes, a non-optimal dispersion process leads to deterioration of the stability of the pastes and of the paints and coatings produced therefrom. The depth of color of the resulting coatings is also not optimal.
Accordingly, it is an object of the present invention to provide new dispersing and wetting agents for the preparation of pigment and/or filler pastes having improved properties.
This object may be achieved with the aqueous compositions according to the invention, which are described hereinafter.